An auxiliary power unit (APU) may be provided with an inlet door that is moveable between a closed position and one or more open positions to allow airflow into the APU and accordingly provide the desired APU functionalities.
In some existing systems, when it is impossible to determine what position the APU inlet door is in with respect to a commanded position, the APU is prevented from starting. A drawback of this approach is that necessary APU power may not be provided during emergency in-flight starts if the inlet door position feedback is failed. In addition, availability of the aircraft is significantly impacted. There is therefore a need for an improved system and method for controlling an APU.